Conventionally, an actuator is known which includes a track member provided with a base extending along a longitudinal direction and a pair of walls erected from opposite ends of the base in a width direction, with a rolling-element rolling groove formed along the longitudinal direction; a moving member assembled movably along the longitudinal direction between the walls, with a load rolling-element rolling groove corresponding to the rolling-element rolling groove formed in the moving member; and a screw shaft passed through a through-hole formed in the moving member, with a screw rolling-element rolling groove formed in the screw shaft, the screw rolling-element rolling groove being spiral in shape.
In such an actuator, rolling elements are interposed, respectively, between the track member and the moving member and between the screw shaft and a nut member attached to the moving member, forming a greasing structure for smooth rolling of the rolling elements.
Various types of such greasing structures are known, including a structure described, for example, in Patent Literature 1, in which a first passage leading to a thread groove of a nut member is formed to pass a lubricant injected through an inlet for use to supply the lubricant to a moving member; and the first passage includes a second passage continuous with the inlet formed in the moving member, a third passage formed in the nut member, a fourth passage formed between the moving member and the nut member, and a fifth passage adapted to supply the lubricant to a rolling element between a track member and the moving member by being communicated with the fourth passage.
Structures such as described above allow the lubricant supplied through the inlet to be supplied directly to the rolling element between the track member and moving member as well as the rolling element between the screw shaft and nut member, making it possible to supply the lubricant stably.